1. Field of the Invention
This invention relates to an orthopaedic measuring and displaying system.
2. Description of the Prior Art
U.S. Pat. No. 4,583,555 discloses a tibia-referenced system for objectively testing the integrity of the anterior and posterior cruciate ligaments of the knee with passive glide (i.e. drawer), active glide, and end point tests. Two simplified forms of the system embody an elongated reference arm with a distal end pad that is fulcrumed against a distal region on the tibia and a proximal reference pad that rests on either the tibial tubercle or patellar bone structure, while a displacement indicator rod slidably mounted on the arm carries another proximal reference pad that rests on the other of these two bone structures adjacent the knee joint. In a third form of intermediate complexity, the second reference structure, instead of the indicator rod, is a second elongated reference arm distally pivotally connected to the other reference arm, each of the two arms carrying a reference pad that rests on a respective one of the tibial tubercle and patellar bone structures; and in this form the relative angular pivotal positions of the arms is translated to a displacement indicator dial that provides a direct readout of anterior or posterior glide. The fourth and most complex form of the system has the distally pivoted reference arms and direct readout displacement indicator dial of the third form, and further includes a case in which the arms are pivoted that is strapped against the tibia, with a force-applying handle extending anteriorly of the case and force-indicating microswitches operatively arranged between the handle and the case to audibly indicate predetermined applied force levels.
The article "In Vivo Knee Stability" by Messrs. Markolf, Graff-Radford and Amstutz in the Journal of Bone and Joint Surgery, Vol. 60A (1978.07) No. 5, pages 664-674, discloses the use of a clinical testing apparatus to record anterior-posterior tibial force versus glide and varus-valgus moment versus angulation during manual manipulation of the knee. A modified dental chair served as the base for the apparatus. When the apparatus was positioned for glide testing, the knee was in 90.degree. of flexion and the subject was seated erect with the thigh secured in an adjustable metal shell clamped to the chair and containing an inflatable pad, with the pelvis slid posteriorly against the seat back, a contoured metal patellar block covered with stiff padding was pressed against the patella and locked in position. The ankle was strapped securely to an adjustable foot rest. The examiner then applied glide force manually. When the glide test was performed with a 20.degree. flexion angle, the foot rest again held the ankle rigidly. A heavy canvas strap behind the knee was used to hold the patella firmly against the pad. To apply glide force, a small, V-shaped, padded, aluminium plate was pressed against the anterior margin of the tibia just below the tibial tubercle and secured by a "VELCRO" strap around the calf. An instrumented force handle was connected to the plate and the glide force was recorded on the y-axis of the recorder. A spring-loaded plunger was positioned on the tibial tubercle and its shaft was connected to a card which passed over a pulley mounted on the shaft of a rotary potentiometer. The output of this potentiometer, which was calibrated to measure glide, was recorded on the x-axis of the recorder. Medial/lateral fixation of the femur was accomplished by medial and lateral femoral condylar clamps with pressure pads. Varus-valgus angulation of the tibia was recorded by a rotary potentiometer mounted on an aluminium frame and strapped to the tibia. The shaft of this potentiometer was connected to a four-bar linkage mounted on a rigid cross-bar fixed to the chair. For the application of medial-lateral force, the subject's shoe was clamped onto an adjustable holding plate. Medial and lateral force handles, screwed into vertical bars perpendicular to the plate, were located at approximately the level of the ankle. The force output was recorded on the y-axis of the recorder. The distance from the line of the applied force to the knee joint line was measured so that the varus-valgus bending moment at the knee could be calculated.
U.S. Pat. No. 4,306,571 discloses a three-plane goniometer including three small rotary potentiometers which are closely spaced together in a unit to measure rotation of the knee about three different axes, namely internal-external rotation angles, flexion-extension angles, and varus-valgus angles. The unit is primarily mounted on a cuff on the outside of the thigh. The mounting assembly for the three-plane goniometer includes a curved yoke where the ends of the yoke curve from the front to the rear, with the goniometer unit being held between the ends of the rearwardly extending arms of the yoke. Extending downwardly from the goniometer is a square rod which slidably engages a square hole in a nylon ball mounted in a two-axis gimbal, which is secured to a cuff strapped to the calf of the leg. Injuries may be diagnosed by comparing the pattern for one leg before injury with the pattern for that leg after injury or by comparing the pattern for one (healthy) leg with that for the other (injured) leg. The goniometer is mounted so that it may be readily reversed and used for both the right and left legs. Associated processing circuitry includes corresponding reversing circuits for conforming the plots for the right and left leg, and also includes special face marking circuitry. Comparative tests may be made for different types of footwear and athletic playing surfaces, and the torque which is produced may be compared to determine the preferred footwear or playing surface.
The article "In Vivo Rotatory Knee Stability" by Messrs. Shoemaker and Markolf in The Journal of Bone and Joint Surgery, Volume 64A, (1982.02), No.2, pages 208 to 216 discloses the use of a clinical testing apparatus to measure active and passive components of torsional stability of the knee, test curves being produced for torque versus internal-external rotation. The apparatus included a dental chair modified with a rigid cross bar, a thick, stationary, horizontal centre-pole and an adjustable vertical centre post. For a torsion test at 90.degree. flexion, the subject's foot was secured to the chair foot-plate with "VELCRO" straps and raised metal shoe-stops clamped tightly against the foot. The knee was strapped firmly against a patellar pad held to the cross-bar with a dual-locking clamp. Tibial rotation was measured by a rotary potentiometer mounted in a housing contoured to fit against the tibial crest and strapped to the leg above the ankle. An additional potentiometer mounted to the heel of the foot-plate measured rotation of the foot. The potentiometer shafts were connected alternately to a four-bar linkage that was free to swing in the anterior-posterior plane through low-friction linear races mounted to the base of the foot-plate. Tibial torque was measured by an electrical torque-cell built into the middle of the shaft of the foot-plate. The distal end of the shaft allowed the foot-plate to be rotated manually with a handle or locked into place with a frictional split-clamp brake. To study 20.degree. of flexion, the foot-plate was mounted to the adjustable vertical post. A contoured wooden block shaped and padded to contact the patella was clamped to the cross-bar, and a "VELCRO" strap held the knee firmly against the block. Medial and lateral femoral condylar clamps co-operated with the patellar block and strap to minimise the rotation of the femur in response to torque applied at the foot. Continuous measurements of applied torque versus induced rotation for movement of the tibia and the foot were plotted on an x-y recorder during cyclic loading by the examiner.
U.S. Pat. No. 4,583,554 discloses a knee ligament testing device for use in testing the anterior cruciate ligament of the knee. The device includes a force application arm and a reference arm which are hinged at a pivot joint. A predeterimined maximum force can be applied to the force application arm by exerting force on a torque limiter inserted in an aperture in the force application arm. The torque limiter ensures that the identical force will be applied on a leg for every test to ensure reproducibility and prevents the application of excessive force to the leg. Displacement of the tibia relative to the femur is sensed by movement of an inner tube relative to an outer tube which is translated into rotational movement of an input shaft of an electrically linear, rotary potentiometer. The change in resistance in the potentiometer is analyzed and converted to a linear measurement which is displayed on a display.
U.S. Pat. No. 4,804,000 discloses an apparatus for electronically measuring ligamentous insufficiencies in the knee, the apparatus including an exoskeletal articulating framework that is secured above the knee to the patient's femur and below the knee to the tibia and has substantially skeletal conforming articulating joint members with measuring means for determining the relative motions of tibia to femur. The measuring means measure, in addition to anterior-posterior glide, varus-valgus laxity and internal-external rotation of the tibia while recording the flexion angle. They include a first radial transducer positioned at the axis of overall knee flexion to measure the flexion angle and alternate second and third radial transducers to selectively measure internal-external rotation or varus-valgus motion. The anterior-posterior glide is measured by a fourth transducer connected to a support linkage of a floating patellar pad positioned at the end of a tibial rod.
Although the apparatus of U.S. Pat. No. 4,306,571, U.S. Pat. No. 4,583,554 and U.S. Pat. No. 4,804,000 are much more portable and compact than the dental chair-based apparatus of the two journal articles, their measuring devices all require to be interposed between two driving elements themselves acting upon or acted upon by bones of the joint.